Right Triangle Slides
Triangle Builders • Lesson 1
60 Minutes
Right Triangles: Perimeter & Area
Discover how to build the outside fence (Perimeter) and count the inside square units (Area) using multiplication and regrouping.
1. Warm-Up
15 mins • Math Review
2. I Do
15 mins • Teacher Model
3. We Do
15 mins • Team Practice
4. You Do
15 mins • Solo Build
Warm-Up
Prerequisite Skill Builder (15 Mins)
Regroup & Multiply
Addition with Regrouping
When the ones add up to 10 or more, trade 10 ones for 1 ten upstairs!
↑ Regroup 1 18 + 15
33
↑ Regroup 1 27 + 19
46
Single-Digit Multiplication
Multiply Base × Height, then find Half (cut in 2)!
6 × 4 = 24
Half of 24 = 12
8 × 3 = 24
Half of 24 = 12
7 × 4 = 28
Half of 28 = 14
6 × 6 = 36
Half of 36 = 18
Check your Warm-Up worksheet section now! 15 minutes complete
Concept
Anatomy of a Right Triangle
Look for the Corner Box!
Height (6 units) Base (6 units) Slant Side (c)
1. Height (\(h\)) & Base (\(b\)) Meet at \(90^\circ\)
The two straight sides that make the L-shape square corner are your base and height.
2. Perimeter is the Outside Path
Add all 3 sides: Side 1 + Side 2 + Side 3.
3. Area is Exactly Half a Rectangle!
Multiply base × height, then divide by 2: (b × h) ÷ 2.
Always find the square corner box □ first to identify Base and Height!
I Do: Step 1
Finding Perimeter with Regrouping
Teacher Model
15 cm 20 cm 25 cm
Sides: 15 cm, 20 cm, 25 cm
Step 1: Set Up Place-Value Column Box
Tens Ones
[ +1 ]
1 5
2 0
+ 2 5
6 0
Ones Column:
5 + 0 + 5 = 10 ones
→ Write 0, Regroup 1 Ten upstairs!
Tens Column:
1 + 1 + 2 + 2 = 6 tens
Total Perimeter = 60 cm
Formula: \( \text{Perimeter} = \text{Side}_1 + \text{Side}_2 + \text{Side}_3 = 15 + 20 + 25 = 60\text{ cm} \)
I Do: Step 2
Finding Area: Multiply & Halve
Area = (b × h) ÷ 2
h = 6 units b = 8 units
Triangle = Exactly Half of 6 × 8 Rectangle!
Step 1: Single-Digit Multiplication
\( \text{Base} \times \text{Height} = 8 \times 6 = \mathbf{48} \)
Step 2: Divide by 2 (Cut in Half!)
\( 48 \div 2 = \mathbf{24}\text{ sq units} \)
Think: Half of 40 is 20, half of 8 is 4 → 20 + 4 = 24
Final Area = 24 square units (units²)
We Do
Guided Team Practice (15 Mins)
Let's solve together!
Right Triangle Garden
h = 7 m b = 6 m slant = 9 m
A. Find the Perimeter (Fence)
\( 7 + 6 + 9 = \mathbf{?}\text{ meters} \)
7 + 6 = 13 → 13 + 9 = 22 meters
B. Find the Area (Grass Seed)
- Base × Height = \( 6 \times 7 = \mathbf{42} \)
- Half of 42 = \( 42 \div 2 = \mathbf{21}\text{ m}^2 \)
Turn to Page 2 in your Student Packet to verify your work with your partner! Great job!
You Do
Independent Practice (15 Mins)
Solo Builder Time
1
Check the Corner
Find the \(90^\circ\) square box to spot your Base and Height.
Don't mix up slant with height!
2
Perimeter Box
Line up all 3 side numbers into your place-value columns and regroup if needed.
Check: Side 1 + Side 2 + Side 3
3
Area Halving
Multiply Base × Height, then cut that number in half.
Area = (b × h) ÷ 2
Target: Complete Problems 1–4 on Page 3 of your packet!
15 Mins
Right Triangle Student Packet
Lesson 1 Packet Triangle Builders • Special Education Math
Right Triangles: Perimeter & Area
Name:
Date:
Anchor Guide • How to Solve Right Triangles
Reference Tool
h = 6 b = 8 slant = 10 □ = \(90^\circ\) Corner (Base & Height meet)
Perimeter (Outside Fence)
\( \text{P} = \text{Side}_1 + \text{Side}_2 + \text{Side}_3 \)
\( 6 + 8 + 10 = \mathbf{24\text{ units}} \) (Use place-value box if regrouping).
Area (Inside Squares)
\( \text{A} = (\text{Base} \times \text{Height}) \div 2 \)
\( 8 \times 6 = 48 \rightarrow 48 \div 2 = \mathbf{24\text{ sq units}} \).
1
Part 1: Prerequisite Warm-Up (15 Minutes)
Review: Multiplication & Regrouping
A. Single-Digit Fact & Halving Drills:
4 × 6 = ______
Half of that = ______
8 × 4 = ______
Half of that = ______
6 × 6 = ______
Half of that = ______
7 × 4 = ______
Half of that = ______
B. Regrouping Calculation Boxes (Show your trade upstairs!):
Problem 1 (Add)
Tens Ones
2 8
+ 1 5
Problem 2 (Add 3 Sides)
Tens Ones
1 4
1 8
+ 2 2
Problem 3 (Subtract)
Tens Ones
5 2
- 1 7
Warm-Up Target: Check solutions with teacher before moving to Guided Practice. Page 1 of 3
2
Part 2: I Do • Guided Model & Notes (15 Mins)
Teacher Led
Guided Fill-In: The 3 Rules of Right Triangles
Rule 1: The Base and Height always connect at the angle corner (\(90^\circ\)).
Rule 2: To find Perimeter, add all sides together.
Rule 3: To find Area, multiply Base × Height and then divide by (cut in half).
3
Part 3: We Do • Guided Partner Practice (15 Mins)
Solve Step-by-Step with Partner
Right Triangle on Grid h = 5 b = 7 slant = 9 Units: cm
A. Find Perimeter (\( \text{P} = 5 + 7 + 9 \))
TO
5
7
+9
1. Add 5 + 7 = 12
2. Add 12 + 9 = ______
Perimeter = ______ cm
B. Find Area (\( \text{A} = (\text{b} \times \text{h}) \div 2 \))
Right Triangle Homework Worksheet
Homework • Lesson 1 Triangle Builders
Right Triangle Builders: Take-Home Practice
Name:
Due Date:
Homework Reminder: Perimeter = Add 3 sides (fence). Area = (Base × Height) ÷ 2 (inside squares).
1
Quick Multiplication & Halving Review
8 × 5 = ______
Half of that = ______
6 × 8 = ______
Half of that = ______
9 × 4 = ______
Half of that = ______
2
Calculate Perimeter & Area
Problem 1: Triangle on Grid Grid Units
5 8 9
A. Find Perimeter
Equation: 5 + 8 + 9
B. Find Area
\( 8 \times 5 = \) ______
Half = sq units
Problem 2: Regrouping Required Inches
16 in 12 in 20 in
Perimeter Box:
TO
16
12
+ 20
Area Calculation:
Base = 12, Height = 16
12 × 16 = 192
Area = 192 ÷ 2
Turn over for word problems and self-monitoring. Page 1 of 2
3
Real-World Triangle Problems
Application
Problem 3: Playground Sandbox Real World
A park builds a right-triangle sandbox with legs of 6 meters and 8 meters, and a long edge of 10 meters.
A. Wood border for sandbox (Perimeter):
Equation: 6 + 8 + 10
Units: meters
B. Play area inside (Area):
Step 1: 6 × 8 = ______
Step 2: Half of that = ______
Units: square meters (m²)
Problem 4: Compare Two Triangles (Subtraction Review) Regrouping Subtraction
Triangle A has a perimeter of 54 cm. Triangle B has a perimeter of 38 cm. How much larger is Triangle A's perimeter?
Subtraction Column Box:
TensOnes
54
- 38
Step 1: Cannot do 4 − 8. Borrow 1 Ten from 5.
Step 2: 5 becomes 4. 4 becomes 14.
Step 3: 14 − 8 = ______; 4 − 3 = ______
Difference = ______ cm
Student Homework Checklist
Solved all multiplication drills
Showed regrouping steps
Wrote unit labels (cm, in, m)
